In a conventional data-processing system, such as a computer and/or a computer network, one or more processors may communicate with input/output (I/O) devices over one or more buses. The I/O devices may be coupled to the processors through an I/O interface such as an I/O bridge, which can manage the transfer of information between a peripheral bus connected to the I/O devices and a shared bus connected to the processors. Additionally, the I/O interface may manage the transfer of information between a system memory and the I/O devices or the system memory and the processors.
An I/O interface can also be utilized to transfer information between I/O devices and main storage components of a host processor. An I/O channel, for example, may connect the host directly to a mass storage device (e.g., disk or tape drive). In the case of a mainframe host processor, the channel is usually coupled to one or more device controllers. Each device controller can in turn be connected to a plurality of mass storage devices.
One example of an I/O interface that is become widely utilized in the data-processing and computer arts is the so-called “Fibre Channel.” In general, features of both channels and networks have been incorporated into a network standard known as “Fibre Channel,” which has been defined by American National Standards Institute (ANSI) specifications, such as X3.230 (1994). Fibre Channel systems attempt to combine the speed and reliability of channels with the flexibility and connectivity of networks.
In general, data in a Fibre Channel network can be transported in packets, which may be two kilobytes or smaller. These packets of data can be referred to as “frames.” “Sequences” include one or more frames. Frames in a sequence are generally assembled at the receiving device in a predetermined order before the sequence can be considered complete.
Fibre Channel is a campus-wide interconnection standard that is designed primarily to interconnect peripherals, mass storage systems such as redundant arrays of inexpensive disks (RAID), imaging and archiving systems, mainframes, engineering workstations, and other high speed devices. Often seen as the successor to the Small Computer Serial Interface (SCSI) standard, Fibre Channel is a high-speed channel that typically uses fiber optics to interconnect computing devices in a relatively local environment, such as a laboratory or a campus. Thus, the Fibre Channel focuses more on providing bandwidth between devices than a completely flexible network. Fibre Channel is a switched technology.
The Fibre Channel interface dedicates circuits for transferring data while allowing other devices to access the channel when it is free. The Fibre Channel interface supports variable length transmissions; it can transmit large blocks of data without dividing the blocks into smaller packets. The speed of Fibre Channel is in the range of 133 Mbit/sec-1062 Mbit/sec. While multimode optical fiber is used most often, single mode optical fiber, coaxial cable, and shielded twisted pair wire are also occasionally used in practice. An example of a Fibre Channel method and system is disclosed in U.S. Pat. No. 6,721,320, which issued on Apr. 13, 2004 to Hoglund et al and is assigned to LSI Logic Corporation based in Milpitas, Calif. U.S. Pat. No. 6,721,320 is incorporated herein by reference.
Another well-known I/O interface is Serial Attached SCSI (SAS). SAS incorporates feature of Small Computer System Interface (SCSI), also known as “skuzzy”, which is a bus protocol that allows various internal and external devices to be connected to personal computers, workstations, servers, and/or other data-processing systems. SAS is a is a point-to-point architecture, distinct from parallel technologies in which devices are connected utilizing shared-access topologies, such as a Fibre Channel arbitrated loop of the SCSI bus. As such, a point-to-point architecture establishes a link directly from the controller to a disk drive or through an expander switching matrix. In shared-access topologies, only two devices can communicate at once. As well, as throughput needs increase, the shared-access medium can become a bottleneck and slow down communication. Shared access topologies also are typically more complex and have arbitration schemes that are more time consuming than point-to-point architectures.
Despite recent advances in such I/O interface technologies, users of I/O interfaces are still faced with some inherent difficulties. For example, when assembling frames for transmission over an I/O interface (e.g., SAS, Fibre Channel, and the like), a user requires flexibility and speed to assemble and transmit the frame data. Conventional I/O methods and systems handle frame transmission utilizing hardware or state machines to assemble and transmit a frame. Custom hardware, on the other hand, is fast, but is not flexible and does not adapt well to changing requirements in assembling a frame. This is one of the advantages of custom hardware, such as, for example, a custom state machine.
Alternative I/O methods and systems permit the processor to manually assemble and transmit each frame. Current hardware solutions do not offer the flexibility required for new interface protocols, because such solutions change quickly or are not defined completely. In practice, much variation exists in how the I/O protocols are handled, thus flexibility is important. Also, utilizing a processor for assembly and transmission of a frame is very slow, inefficient, and produces poor performance results. Additionally, processor interactions can cause poor protocol performance. A slow processor, for example, may be tied directly to the performance of the protocol.
It is therefore believed that a solution to such drawbacks lies in the development of a processor that can actually assemble frames in a completely generic fashion and then send the frames over a link, while processing and assembling the next frame for transmission. Such features are not known in conventional frame management methods and systems, but are inherent to the embodiments disclosed herein.